Exposure apparatus for manufacturing fluorescent screens of colour picture tubes

ABSTRACT

A composite correction lens means including two superposed correction lenses is used to cause the exposure light to travel along a path approximating the actual locus of an electron beam in a colour picture tube. Each correction lens has a wedge shaped sectional configuration. A shield disc having a perforation for exposing a selected area of the fluorescent screen is disposed between the composite correction lens means and the fluorescent screen. The relative angular position between the shield disc and the composite correction lens means is made variable.

United States Patent Yamazaki et al.

EXPOSURE APPARATUS FOR MANUFACTURING FLUORESCENT SCREENS OF COLOUR PICTURE TUBES Inventors: Eiichi Yamazaki, lchihara; Koichi Maruyama; Toshio Ueda, both of Mobara; lwao Ogura, Tokyo, all of Japan Assignee: Hitachi, Ltd., Tokyo, Japan Filed: Dec. 12, 1973 Appl. No.: 424,092

Foreign Application Priority Data Dec. 25. 1972 Japan 47-129272 U.S. Cl. 354/1 Int. Cl. G03b 27/00 Field of Search 354/11 References Cited UNITED STATES PATENTS l-lerzfeld et al. 354/1 [451 May 13, 1915 3,736,848 6/1973 Tsuneta et a1. 354/1 3,738,234 6/1973 Barten et al. 354/1 3,783,754 1/1974 Takemoto et 354/] Primary Examiner-Richard M. Sheer Attorney, Agent, or Firm-Dike, Bronstein, Roberts, Cushman & Pfund 5 7] ABSTRACT A composite correction lens means including two superposed correction lenses is used to cause the exposure light to travel along a path approximating the actual locus of an electron beam in a colour picture tube. Each correction lens has a wedge shaped sectional configuration. A shield disc having a perforation for exposing a selected area of the fluorescent screen is disposed between the composite correction lens means and the fluorescent screen. The relative angular position between the shield disc and the composite correction lens means is made variable.

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saw u or 6 EXPOSURE APPARATUS FOR MANUFACTURING FLUORESCENT SCREENS OF COLOUR PICTURE TUBES BACKGROUND OF THE INVENTION This invention relates to an exposuredevice utilized to manufacture a fluorescent screen of a colour picture tube.

As is well known in the art, a fluorescent screen of a shadow mask type colour picture tube is formed with regularly arranged phosphor dots or stripes by means of photographic technique. Ideally. the path of the exposure light should coincide with the locus of the electron beam in the colour picture tube in order to reproduce pictures of high quality. Accordingly. it is important to control the path of the exposure light during the exposure operation by bending the path. To provide such a control. correction lenses having continuous or discontinuous curved surfaces of complicated construction have been used. With such correction lenses it has been impossible to completely align the landing point of the electron beam spot with the phosphor dot or phosphor stripe. Moreover, correction lenses of complicated construction are difficult to manufacture because a large cost. long period and a large number of process steps are required. According to an improved method. a slit is interposed between a source of light and the correction lens and the slit is moved relative to the source of light and the correction lens for partially exposing the fluorescent screen thereby improving the accuracy of the landing of the electron beam spot upon the phosphor dot. However. this method requires to use a special point light source of high brightness so that the exposure apparatus is complicated and the movement of the light source results in errors.

SUMMARY OF THE INVENTION It is an object of this invention is to provide an improved exposure apparatus utilized to manufacture a fluorescent screen of a colour picture tube and capable of improving the accuracy of the landing of the electron beam spot upon phosphor dots or stripes thus producing pictures of high qualities.

Another object of this invention is to provide an improved exposure apparatus utilized to manufacture a fluorescent screen of a colour picture tube and capable of providing an improved wide angle colour picture tube in which colour shading at the peripheral portion of the tube is eliminated.

According to this invention these and other objects can be accomplished by providing exposure apparatus for manufacturing a fluorescent screen of a colour picture tube ofthe class wherein a correction lens is interposed between a source of light and the fluorescent screen. characterized in that the correction lens takes the form of a composite correction lens means including two superposed correction lenses. that a shield member provided with a perforation for exposing a selected area of the fluorescent screen is positioned between the fluorescent screen and the composite correction lens means. and that the relative angular position of the composite correction lens means and the shield member is made variable.

Each correction lens has a wedge shaped sectional configuration with a curved effective surface or a rectangular shaped sectional configulation with inclined surfaces divided by discontinuous border lines on its effective surface. Not only the relative angular position between the shield means and the composite correction lens means but also the relative angular position between two correction lenses are made variable.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic sectional view of a prior art exposure apparatus for manufacturing a fluorescent screen of a colour picture tube;

FIG. 2 is a diagram showing a manner of landing of an electron beam spot upon a phosphor dot;

FIG. 3 is a vector diagram to explain the landing condition of the electron beam spot shown in FIG. 2;

FIG. 4A shows a plan view ofa wedge shaped correction lens;

FIG. 4B shows a cross-section of the lens shown in FIG. 4A taken along a line IVB IVB'.

FIG. 4C shows a cross-section of the lens shown in FIG. 4A taken along a line IVC IVC;

FIG. 5A shows a plan view of one embodiment of the composite correction lens of this invention;

FIG. 5B shows a sectional view of the lens assembly shown in FIG. 5A taken along a line VB VB;

FIG. SC shows a sectional view of the lens assembly shown in FIG. 5A taken along a line VC VC;

FIG. 6A is a plan view showing a modified composite correction lens of this invention;

FIG. 6B is a sectional view of the lens assembly shown in FIG. 6A taken along a line VIB VIB;

FIG. 6C is a sectional view of the lens assembly shown in FIG. 6A taken along a line VIC VIC;

FIG. 7A is a plan view showing another form of the composite correction lens of this invention;

FIG. 7B is a sectional view of the lens assembly shown in FIG. 7A taken along a line VIIB VIIB;

FIG. 7C is a sectional view of the lens assembly shown in FIG. 7A taken along a line VIIC VIIC;

FIG. 8A is a plan view of a composite correction lens showing the relative position of lenses which is useful to explain the direction of correction of a correction vector;

FIG. 8B is a sectional view of the lens assembly shown in FIG. 8A taken along a line VIIIB VIIIB;

FIG. 8C is a sectional view of the lens assembly shown in FIG. 8A taken along a line VIIIC VIIIC,

FIG. 9 is a perspective view of the essential elements of an exposure apparatus embodying the invention;

FIGS. 9A. 9B and 9C show perspective views of shield discs having openings of different configurations,

FIGS. 10A shows still another embodiment of the composite correction lens embodying the invention;

FIG. IOB is a sectional view of the lens assembly shown in FIG. 10A taken along a line XB XB and FIG. 10C is a sectional view of the lens assembly shown in FIG. 10A taken along a line XC XC.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the manufacture of a fluorescent screen of a shadow mask type colour picture tube. it is common to use an exposure apparatus 1 usually termed a lighthouse and comprising a source of light 2 and a correction lens 3, as shown in FIG. 1. A face plate or panel provided with a shadow mask 4 is mounted on the exposure apparatus 1. The correction lens 3 functions to modify the path of the exposure light emanated from the source of light 2 such that the light travels along a path approximating the actual locus of the electron beam in the colour picture tube. whereby the fluorescent screen, not shown. coated on the inner surface of the face plate 5 is exposed to light transmitting through the shadow mask 4. The exposed fluorescent screen is then fixed by photographic technique to form phosphor dots. The correction lens generally has continuous or discontinuous curved surfaces of complicated configurations. This provides fairly satisfactory correction. With recent trend of using wide angle colour picture tubes, it becomes difficult to accurately make the path of the exposure light to approximate the actual locus of the electron beam, especially at the peripheral portion of the effective area of the flourescent screen.

Considering the misalignment of an electron beam spot landing on a phosphor dot in the effective area of a fluorescent screen with reference to FIGS. 2 and 3, the vector A representing the misalignment is decomposed into a horizontal component Ax and a vertical component Ay which are expressed as follows as functions of the position.

m n AX m O n 0 lmn x y (1) co co m n Ay H120 m o 2mn x y (2) where C and C-,,,,,, represent coefficients and each of m and n equals to 0,1, 2. 3

However, it is almost impossible to obtain simultaneous solutions of equations Ax and Ay so that it is impossible to obtain a correction vector that satisfies simultaneously equations Ax and Ay and to utilize such vector in the design of the correction lens. Thus, it has been necessary to use an approximate solution for the design of the correction lens. This makes more difficult to provide adequate correction for the peripheral portion of the fluorescent screen as the angle of the funnel of the colour picture tube increases.

According to this invention. in said equations l and (2) a small area that can be represented by the following equations is considered AX a (3) Ay C (4) where C and C are constants, and the maximum value of the misalignment in this small area is considered over the entire area of the fluorescent screen. More particularly, the effective area of a fluorescent screen is considered to be an aggregate of such small areas. In a local aggregate, it is considered that the vector of misalignment is independent of the position and one half of the maximum value of the vector of misalignment in a local aggregateis used to design a correction lens.

Thus. a value lAl max expressed by an equation lAl is taken and the correction lens is desi ned to correct an amount of misalignment equal to l I max/2.

In the small area. since Ax and Ay may be considered constants l A I max is also a constant. As a come quence. the correction lens 11 will have a wedge shaped cross-sectional configuration in which its upper or effective surface is inclined in the direction of .r alone as shown in FIGS. 4A. 4B and 4C. When neglecting the thickness of the lens. the correction lens II will have a configuration ofa simple prism, the inclined surface being curved to eliminate the effect of thickness.

When two such correction lenses 1] are superposed one upon the other. it is possible to correct misalignment A in all small areas in the entire effective area of the fluorescent screen. Thus, two lenses l2 and 13, each identical to lens II are superposed one upon the other as shown in FIGS. 5A, 5B and SC to provide a composite correction lens having a correction effect for a misalignment expressed by IAI max/2 IAI max/2 IAImax.

If the two lenses are combined as shown in FIG. 6 with their upper or effective surfaces inclined in the opposite direction, the correction effects of the two lenses would cancel each other as shown by the following equation 1K1 max/2 IXI max/2 0 thus providing a co ndition wherein the amount of misalignment is zero, A 0.

Furthermore, if one lens were rotated by an angle rb, with respect to the other, correction for a corresponding misalignment could be made. This arrangement permits continuous correction for the amounts of mis alignment in a range from 0 to IA max.

Since A is a sealer quantity. it is necessary to correct not only its magnitude but also its direction. One example of such correction is illustrated in FIG. 8. Thus, the assembly shown in FIG. 7A is rotated by an angle :1) with the relative angle d between two lenses unchanged whereby the direction of correction is varied while the magnitude thereof established by the relative angle d), maintained constan t Accordingly. it is possible to correct misalignment A in any small areas in the entire area of the fluorescent screen of the colour picture tube.

FIG. 9 shows one example of the novel exposure apparatus utilizing the composite correction lens described above. The exposure apparatus shown in FIG. 9 comprises a lower correction lens 15 having a wedge shaped sectional configuration and rotated by a gear or roller 18, an upper correction lens 14 having similar sectional configuration and rotated by a gear or roller 17 and a shield disc 20 positioned above the correction lens 14 and rotated by a gear or roller 21, the disc 20 being provided with a perforation 25 which projects the exposure light from a source oflight 19 only upon a desired area on the fluorescent screen coated on the inner surface of the face plate 16 through shadow mask 22. By performing such exposure operation for the entire portion or selected portions of the fluorescent screen it is possible to perfectly correct the misalignment of the electron beam spot and the phosphor dots over the entire surface of the fluorescent screen. Thus it is possible to prevent degradation of the picture quality due to the colour shading caused by such misalignement. In this manner, the invention is especially suitable for wide angle colour picture tubes.

It will be clear that the perforation 25 may take any desired configuration as shown in FIGS. 9A, 9B and 9C that is elliptical, polygonal or sector shape. so long as the perforation can project the exposure light upon the desired area of the fluorescent screen.

In addition to rotate lenses l4 and I5 and shield disc as has been described hereinabove. it is also possible to adjust them in the vertical direction to provide more accurate correction.

Increase in the exposure time caused by the provision of the shield disc which limits the exposure light projected upon the fluorescent screen can be alleviated by the concurrent use of a correction lens having both continuous and discontinuous curved surfaces. Although use of the composite correction lens increases the required exposure time, improvement of the accuracy of correction overcomes this disadvantage.

FIG. shows another embodiment of the composite correction lens of the invention. Correction lenses shown in FIGS. 4 through 8 had a wedge shaped configuration and their upper surface were curved to eliminate the effect of thickness. However, in the correction lens shown in FIG. 10, the upper or effective surface of the correction lens is shaped in the form of saw teeth with discontinuous border lines 23 between inclined flat surfaces 24. With this construction since it is not necessary to consider the effect of the thickness it is not necessary to incline the upper or effective surface of the lens. Respective surfaces 24 may have the same angle of inclination so that it is possible to readily manufacture the correction lens. As can be noted from FIG. [0A, the border lines 23 and surfaces 24 of the lower correction lens 27 are skewed with respect to those of the upper correction lens 26 which is equivalent to relative rotation of two correction lenses shown in FIG. 7.

As has been described hereinabove, the invention provides an improved exposure apparatus utilizing a composite correction lens including two superposed correction lenses so that by adjusting the relative position of these lenses it is possible to adjust the direction of refraction as well as the intensity of the exposure light. thus enabling to improve the accuracy of alignment of the electron beam spot with the phosphor spot of the fluorescent screen of not only relatively narrow angle colour picture tubes but also wide angle colour picture tubes. This prevents formation of colour shading and improves picture quality.

While the invention has been described in connection with a fluorescent screen having dot shaped phosphors, it should be understood that the invention can also be applied with equal result to fluorescent screens having stripe shaped phosphors.

What is claimed is:

l. In an exposure apparatus for manufacturing a fluorescent screen of a colour picture tube of the class wherein a correction lens is interposed between a source of light and an assembly of a shadow mask and panel on which said fluorescent screen will be developed, the improvement which comprises composite correction lens means including at least two correction lenses. a shield member positioned between said composite correction lens means and said assembly, said shield member provided with a perforation for exposing a selected area of said panel, and means for varying the relative angular position of said composite correction lens means and said shield member for moving said selected area over a selected portion on said panel corresponding to the correction provided by said lens means.

2. An exposure apparatus according to claim I wherein each of said correction lenses of said composite lens means has a wedge shaped sectional configuration and the effective surface of the lens is curved.

3. An exposure apparatus according to claim I wherein each correction lens of said composite lens means is provided with means for rotating the same.

4. An exposure apparatus according to claim 3 which further comprises means for rotating said composite lens means while maintaining the corrective lenses thereof at a constant angular relationship.

5. An exposure apparatus according to claim 1 wherein each of said correction lenses of said composite lens means has a rectangular shaped sectional configuration and effective surface of the lens.

6. Apparatus according to claim 1 and wherein said shield member is selected from a plurality of such said shield members having different perforations and adapted to be successively used to expose a plurality of said selected portions on said panel.

7. In an exposure apparatus having a light source and a correcting lens means, for manufacturing a fluorescent screen of a color picture tube having a shadow mask and a face panel on which the fluorescent screen is to be developed, the improvement comprising:

means for supporting the panel portion with the shadow mask in position;

a light source assembly positioned to expose the inner surface of the panel portion through the mask;

a complex lens system having at least two correcting lenses to approximate the light path from said light source to an actual electron beam path of a color picture tube in operation;

a shield member provided with a perforation limiting light exposure to a selected inner surface area of the panel by confining the light emanated from said light source through said perforation; and

a driving system including a plurality of individual driving means to give a rotary motion to each of said correcting lenses and said shield member so as to adjust a relative angular position thereof;

whereby the light emanated from said light source assembly is approximated to the actual electron beam of the color picture tube through said complex lens system and lands with high accuracy on the selected inner surface area of the panel through said perforation on said shield member via the shadow mask to form a fluorescent screen exposure on the panel. 

1. In an exposure apparatus for manufacturing a fluorescent screen of a colour picture tube of the class wherein a correction lens is interposed between a source of light and an assembly of a shadow mask and panel on which said fluorescent screen will be developed, the improvement which comprises composite correction lens means including at least two correction lenses, a shield member positioned between said composite correction lens means and said assembly, said shield member provided with a perforation for exposing a selected area of said panel, and means for varying the relative angular position of said composite correction lens means and said shield member for moving said selected area over a selected portion on said panel corresponding to the correction provided by said lens means.
 2. An exposure apparatus according to claim 1 wherein each of said correction lenses of said composite lens means has a wedge shaped sectional configuration and the effective surface of the lens is curved.
 3. An exposure apparatus according to claim 1 wherein each correction lens of said composite lens means is provided with means for rotating the same.
 4. An exposure apparatus according to claim 3 which further comprises means for rotating said composite lens means while maintaining the corrective lenses thereof at a constant angular relationship.
 5. An exposure apparatus according to claim 1 wherein each of said correction lenses of said composite lens means has a rectangular shaped sectional configuration and effective surface of the lens.
 6. Apparatus according to claim 1 and wherein said shield member is selected from a plurality of such said shield members having different perforations and adapted to be successively used to expose a plurality of said selected portions on said panel.
 7. In an exposure apparatus having a light source and a correcting lens means, for manufacturing a fluorescent screen of a color picture tube having a shadow mask and a face panel on which the fluorescent screen is to be developed, the improvement comprising: means for supporting the panel portion with the shadow mask in position; a light source assembly positioned to expose the inner surface of the panel portion through the mask; a complex lens system having at least two correcting lenses to approximate the light path from said light source to an actual electron beam path of a color picture tube in operation; a shield member provided with a perforation limiting light exposure to a selected inner surface area of the panel by confining the light emanated from said light source through said perforation; and a driving system including a plurality of individual driving means to give a rotary motion to each of said correcting lenses and said shield member so as to adjust a relative angular position thereof; whereby the light emanated from said light source assembly is approximated to the actual electron beam of the color picture tube through said complex lens system and lands with high accuracy on the selected inner surface area of the panel through said perforation on said shield member via the shadow mask to form a fluorescent screen exposUre on the panel. 